To cut it down, you'd need to fabricate a blanking plate which could be bolted where the original steering locking mechanism goes. That would take about an inch off the thing. From there, you could relocate it to the side of the headlamp or down near the coils.

thanks a lot for your help. finally i decided to put another ignition switch that is much smaller than yamaha's one and to fit it like casper did. I'll put a plug there that appeared in newer models of seca2.